(1) Field of the invention
The present invention relates to a rotor blade, and to an aircraft provided with a blade.
More particularly, the blade may be a blade of a propulsive propeller of an aircraft, or a blade of a lift rotor of a rotorcraft, or of a yaw control rotor of such a rotorcraft. Nevertheless, such a blade may be used for other types of rotor in the context of a compressor blade, a wind turbine blade, a fan rotor, or indeed a rotor for propelling a ship, for example.
(2) Description of Related Art
In its rotary motion, a blade is subjected to a torsor, i.e. in strength-of-materials terms, to a general resultant force and to a resultant moment at each point. Consequently, such a blade is subjected in particular to a centrifugal force and also to multiple loads due to flapping, to drag, and to twisting movements; where twisting is caused in particular by changes of pitch seeking to modify the angle of inclination of the blade relative to the plane of the hub supporting the blade. Naturally, the forces give rise to bending and twisting moments.
The forces and moments to which the blade is subjected as a result in particular of centrifugal force and of twisting stresses thus need to be transmitted to the hub by the blade.
The means for fastening the blade to the hub are therefore subjected to forces and to moments that can be destructive, where the term “load” is used below to designate said forces and/or said moments, for reasons of simplification.
Conventionally, a blade comprises a shell sometimes referred to as a “covering” or indeed an “outer covering”.
The shell is provided with a suction-side wall and a pressure-side wall that extend from a leading edge first zone to a trailing edge second zone. In a blade made of composite materials, the shell may have a suction-side wall and a pressure-side wall that are secured to each other, each comprising at least one layer of fabric based on fibers of high mechanical strength that are embedded in a matrix. The suction-side wall and the pressure-side wall may be made separately and then joined together, or they may be made jointly, e.g. by winding.
The shell is hollow so that it can receive generally at least one spar serving in particular to take up the centrifugal loads that act on the blade in rotation, and at least one filler element. Each spar may be made of composite material, being made using fibers that are embedded in a matrix, the fibers describing a U-shaped structure, for example.
Furthermore, it is common practice to provide the trailing edge zone of the shell with a ledge in order to reinforce the blade in particular against drag stresses.
Document EP 0 570 527 describes a blade provided with a spar including at least one front torsion box element that is elongate in the span direction, and at least one rear torsion box element that is elongate in the span direction, the boxes being connected together by a chordwise shear web.
The spar is made of two casing halves adhesively bonded together back-to-back.
Document FR 1 579 886 describes a blade provided with a spar constituted by a box-shaped hollow structure that comprises two opposite U-shaped elements that are engaged one in the other.
Document EP 0 307 288 describes a rotor blade provided with an attachment device using bushings.
Document U.S. Pat. No. 3,694,104 presents a turbine engine blade.
Document EP 0 353 672 describes a propeller blade made of fiber-reinforced material.